As one type of three-dimensional television systems that can be viewed from any point, IP using a refractive index distribution lens group arranged on a plane has been known (for example, see Japanese Patent Laid-Open No. 10-150675). The refractive index distribution lens is herein also referred to as a GRIN lens or simply as a GI lens.
FIG. 30 shows a configuration of a three-dimensional image pickup apparatus in Japanese Patent Laid-Open No. 10-150675.
In FIG. 30, reference numerals 1211, 1212, . . . , 121n denote optical fibers, and reference numeral 122 denotes a television camera that picks up the entire images of the optical fibers.
The optical fibers 1211, 1212, . . . , 121n have refractive index distribution with a higher refractive index at a portion closer to the center, and when parallel lights enter these optical fibers, the lights meander and form an image on a specific point. Then, the optical fibers 1211, 1212, . . . , 121n have lengths set so that an image forming position of an erect image is an end surface of each optical fiber.
Even if the optical fibers 1211, 1212, . . . , 121n are arranged so that incident and emission end surfaces of each optical fiber are two-dimensionally placed on one plane as shown in FIG. 30 to form a lens group, the optical fibers do not interfere with each other, and substantially the same advantage can be obtained as in providing an optical barrier. Further, an erect image is obtained on the emission end surface, and thus a correct three-dimensional image can be reproduced rather than a false image with inverted irregularities.
In recent years, distributed refractive index lenses using inexpensive resin material has been developed. A method for fabricating a distributed refractive index lens includes a method for fabricating a distributed refractive index waveguide in a simple process of installation of a mask for adjusting the amount of light and light irradiation using photopolymerization of monomer in an optical medium to change a refractive index (for example, see FIG. 1 of Japanese Patent Laid-Open No. 60-64310).
There is also a method using the photopolymerization reaction as in Japanese Patent Laid-Open No. 60-64310, for fabricating a waveguide type lens having concentric circular refractive index distribution by ultraviolet irradiation from two different directions (for example, see FIG. 1 of Japanese Patent Laid-Open No. 60-175010.
There is also a method using the photopolymerization reaction as in Japanese Patent Laid-Open No. 60-64310, for fabricating an optical waveguide with refractive index distribution by changing the amount of light applied. (for example, see FIG. 1 of Japanese Patent Laid-Open No. 1-134310).
However, as shown in FIG. 30, the configuration in which the optical fibers are arranged in a matrix takes time for alignment of optical axes and is low in productivity and expensive.
For a projector or the like, a heat-resisting lens is required because a projected part is heated to a high temperature, but a resin lens using a conventional photopolymerization reaction has no heat resistance to 80° C. or more, and cannot be used for a projector.
With the conventional fabrication method of the distributed refractive index lens in Japanese Patent Laid-Open No. 60-64310, Japanese Patent Laid-Open No. 60-175010, and Japanese Patent Laid-Open No. 1-134310, a single piece of waveguide type refractive index distribution lens can be fabricated, but one distributed refractive index lens only can be fabricated at a time because of the process with the chemical reaction caused from surroundings.
Thus, producing IP panels using the distributed refractive index lenses fabricated by these conventional fabrication methods requires an assembling step of adjusting optical axes of 10,000 or more distributed refractive index lenses and arranging the lenses in a matrix, and thus the panels are low in productivity. For this reason, even if the resin material is inexpensive, the panels become expensive as in the case of using conventional GRIN lenses made of glass or distributed refractive index optical fibers.